1. Field of the Invention
The invention relates to the field of bicycle transmissions and in particular to transmissions designed to substitute the conventional chain transmission with one that provides a continuously variable transmission ratio.
2. Description of the Prior Art
Frictional transmissions are known in the art. Duryea, "Bicycle," U.S. Pat. No. 333,936 (1886), describes a transmission for a bicycle comprising a pedal crank J, combined with a series of gears J1, K1, K2 and L1. Wheel A is frictionally driven by pulley wheel L2. Wheel is supported between drive pulley L2 and two pulley wheels F and I each disposed at opposing ends of an arm H and supported by a standard D. Duryea shows a three-pulley wheel system inside the rim of a supported wheel, driven through a direct geared transmission from a pedal crank as opposed to a chain drive transmission as commonly used with current bicycles. Duryea however depends on the use of a complicated and unreliable direct gear transmission between pedal crank J and drive pulley wheel L2.
Mead, "Device for Changing Speed," U.S. Pat. No. 168,912 (1875), shows an infinitely variable transmission, having power transferred from a drive shaft A to a driven shaft B by a pair of conically shaped plates which are rotatively coupled together by means of an idler assembly D--D which is axially displaceable on shaft C. Idler wheels D--D are rigidly coupled together on shaft C and, therefore, function as if they were a single wheel, notwithstanding the fact of their spatial displacement from each other. Mead appears to operate with respect to the two conical surfaces in idler wheel D, but there does not appear to be any means which would allow wheels D of Mead to rotate out of the plane of FIG. 1 to allow for freewheeling or a neutral position which is essential in a practical bicycle transmission.
Schmelzer, "ii Friction Drive Mechanism," U.S. Pat. No. 2,074,868 (1937), describes a frictional drive system which provides a smooth gradual acceleration of a rotating member. In FIG. 1, power is supplied through a drive shaft 21 for rotating a driver plate 24. Driver plate 24 has a conical driving surface. Driven plate 41 is also provided with a substantially conical face 42. A friction wheel 36 is axially displaceable on shaft 32 and provided to change the coupling ratio between the driver and driven disks. However, shaft 32 is not able to rotate to allow the idler wheel to pivot out of contact with the driver and driven plates to permit free rotation.
Johnson et al., "Variable Speed Transmission Device," U.S. Pat. No. 2,325,323 (1943), shows in FIGS. 1-4 a drive shaft 25 coupled to a driver plate 23 having a conical engaging surface 24. Torque is transferred from driver plate 23 to driven plate 16 which has a conical engaging face 17. Driven plate 16 is rotatively coupled to a driven shaft 20. Transfer of torque is by means of a transmission ring or idler 53 rotatively supported from an arm 39. Arm 39 is displaceable on a threaded control rod 32 for varying the coupling ratio between the drive shaft and driven shaft. Transmission ring 53 is pivotable by virtue of the arcuate slots 30 and adjustment screw 68. This adjustability is intended, however, to provide adjustment to the contact force of the transmission ring with the conical surfaces and it is not intended to provide a means for freewheeling.
Prager, "Friction Gear," U.S. Pat. No. 3,242,748 (1966), shows a steplessly variable friction gear transmission. Prager was cited for showing a mounting for transmission roller 23 as being coupled to a bearing ring 29 through needle bearing 30. Bearing ring 29 is coupled to shaft 28 through an eyelet projection 31 of adjuster 26. Thus, roller 23 is free to rotate relative to shaft 28, similar to your own system.
While Prager would, at a superficial glance, seem to allow for idler roller 23 to rotate out of the plane in FIG. 21, in fact, the negative cone surfaces of disks 10 and 18 prevent it and keep idler wheel 23 jammed in position. Therefore, Prager does not contemplate the possibility of freewheeling in the transmission.
Aranceta-Angoitia, "Transmission for Bicycles," U.S. Pat. No. 4,900,046 (1990), was cited for showing a conventional bicycle wherein wheel rim 27 is frictionally driven by an outlet pinion 25 through engagement with a coupling track 26.
Therefore, what is needed is some type of frictional transmission which provides smooth and positive responses and continuously variable transmission ratios in combination with user-selective freewheeling, which is essential in a bicycle transmission.